1. Field of the Invention
The present invention relates generally to surgical cutting instruments and, more particularly, to surgical cutting instruments having an elongate inner member rotatably disposed within an elongate outer tubular member having a cutting window at a distal end which cooperates with or permits the inner member to cut or abrade bodily tissue.
2. Discussion of the Related Art
Surgical cutting instruments in which an elongate inner member is rotated within an elongate outer tubular member have become well accepted in surgical procedures where access to the surgical site is gained via a narrow portal or passage. Typically, the outer tubular member includes a distal end with an opening for defining a cutting port or window and the inner member includes a distal end with a cutting tip for engaging bodily tissue via the opening. Proximal ends of the inner and outer members are commonly secured to hubs which attach to a handpiece having a motor for rotating the inner member relative to the outer tubular member. The distal end of the inner member can have various configurations dependent upon the surgical procedure to be performed, with the opening in the distal end of the outer tubular member being suitably configured to cooperate with the particular configuration of the distal end of the inner member to cut, resect or abrade tissue. Often the inner member is tubular so that the loose tissue resulting from a cutting, resecting or abrading procedure can be aspirated through the hollow lumen of the inner member.
While most of the aforementioned surgical cutting instruments have a straight, elongate outer tubular member and a straight, elongate inner tubular member concentrically disposed in the outer tubular member, angled configurations have been produced in which respective axes of the distal tips of the inner and outer tubular members are offset or bent at a fixed angle relative to respective axes of the proximal ends of the inner and outer members. Examples of such fixed-angle, rotary tissue cutting instruments are shown in U.S. Pat. No. 4,646,738 to Trott and U.S. Pat. No. 5,152,744 to Kraus et al. Variable-angle rotary tissue cutting instruments, such as that described in U.S. Pat. Nos. 5,411,514 and 5,601,586 to Fucci et al, permit the user to bend the outer tube to a user-selected angle while still enabling the inner tube to be selectively inserted into and removed from the outer tube; however, known fixed-angle and variable-angle rotary tissue cutting instruments typically have a bend with a radius of curvature on the order of about 2 to 4 inches and are typically not capable of being bent beyond 15.degree.. While the relatively small bend angle and relatively large radius of curvature of these angled tissue cutting instruments is generally suitable for most types of arthroscopic surgery, such instruments are of little use in certain types of head and neck surgery because they are not able to access surgical sites such as the maxillary sinus area which is normally accessed with hand instruments such as ball elevators and suction probes having bend angles of about 40.degree. and radii of curvature on the order of 1.5 inches or less. Accordingly, it would be desirable for a rotary tissue cutting instrument to operate over an increased range of bend angles while at the same time reducing the radius of curvature of the bend for use in head and neck surgery.
In straight rotary tissue cutting instruments, the elongate tubular body or shaft of the inner member is generally integrally formed with the cutting tip and the proximal end of the shaft is generally permanently affixed to a plastic hub. In the case of fixed-angle rotary tissue cutting instruments, however, a flexible coupling is generally interposed between the tubular drive shaft and the cutting tip. In U.S. Pat. No. 5,620,415 to Lucy et al, U.S. Pat. No. 5,620,447 to Smith et al and U.S. Pat. No. 5,152,744 to Kraus et al, the flexible coupling is merely a portion of the inner member which is provided with relief apertures formed in the cylindrical surface to enable the inner member to bend as it rotates. In U.S. Pat. No. 5,529,580 to Kusunoki et al, U.S. Pat. No. 4,646,738 to Trott, U.S. Pat. No. 5,437,630 to Daniel et al, and U.S. Pat. Nos. 5,286,253, 5,411,514 and 5,601,506 to Fucci et al, the flexible coupling is formed of a plurality of counter-wound coiled metallic springs bonded to and interposed between the tubular body and the cutting tip.
One disadvantage of known flexible couplings is their inability to transmit sufficient torque at high speeds through angles much greater than 15.degree. and bend radii less than 2.0 inches. In the case of flexible couplings in the form of coiled springs, there is also the possibility that gaps will develop between the coils as the coupling bends thereby resulting in a decrease of vacuum through the lumen of the inner member and a diminution of the ability of the instrument to aspirate loose tissue through the lumen. Another disadvantage associated with the use of a coiled springs as flexible couplings is the tendency of such members to require tightening or preloading when torque is applied before they are capable of transmitting the torque to the cutting tip. Also, coiled metallic springs have a tendency under certain loading conditions to relax or unwind, and thus expand, thereby increasing the possibility of the inner member binding within the outer member.